Obesity in American children is caused in part by their insufficient physical activity. Neighborhood features that tend to inhibit physical activity in children include lack of open spaces to play, lack of recreational equipment, and fear by parents for the safety of children playing outdoors. When such features are present parents are likely to require that children stay indoors, and children's time indoors is often spent watching television - which has itself been shown to increase obesity rates in children. These neighborhood features are common in low income, inner-city neighborhoods. We propose a pilot study to assess whether an intervention that changes these neighborhood features is followed by increases in physical activity in children. Our intervention will be conducted in an inner-city neighborhood in which schoolyards are currently fenced and locked. It will consist of opening one neighborhood schoolyard, providing basic recreational equipment, and providing attendants who will monitor children to prevent vandalism, minimize the risk of injury, and prevent fights among children. A matched school in which the schoolyard is fenced and locked will serve as a control. The effect of the intervention on the physical activity of children in 2nd through 5th grade will be evaluated by: 1) records of attendance by children at the intervention schoolyard, 2) direct observational measurement of the degree of physical activity in children attending the intervention schoolyard and in the neighborhoods surrounding the control and intervention schools, and 3) surveys of children enrolled in the intervention and control schools assessing the amount of time they spend watching television and in similar sedentary activities.